NATURAL GAS EXPLOSIONS IN HUTCHINSON, KANSAS: ANALYSES OF PRESSURE AND FLOW DATA

Natural gas eruptions occurred in Hutchinson on January 17, 2001, followed by the detection of gas leakage in a cavern in the Yaggy Gas Storage facility located nearby. Thereafter, a series of vent wells were drilled in and around Hutchinson to provide additional pathways to bleed the released gas. These wells were monitored over the next year and a half by recording a series of shut-in pressure surveys, a build-up test, and limited surface flow-rate measurements.

Subsurface pressure at the 3-Fingers zone was periodically mapped using surface shut-in pressure data and fluid-column heights in the vent wells. These maps indicate that pockets still remain pressurized, sub-hydrostatically, as of July 2002. Though sub-hydrostatic, the pressure in one pocket is close to 190 psi. Overlaying regional dip maps on the sub-surface pressure maps reveal that the pressurized pockets align along the structural highs in most places. Build-up tests were carried out in one of the most active wells (OB#2), and the calculated permeability was quite low (3 md). Decline curve analyses was carried out on some wells and it indicated that boundary dominated flow became active in most wells soon after their opening.

Results from the engineering studies are consistent with the current geologic model, i.e., the released gas traveled along a pre-existing stress-induced fracture system, located along the structural high, whose permeability declined with pressure release thus leaving behind pockets of residual gas. Also, it helped to monitor the effectiveness of vent wells, and to formulate a plugging strategy.